Optical sheet lamination

ABSTRACT

In an optical sheet  10  having a prism surface  16  formed by providing unit prisms  14  on the upper surface of a transparent base material  12,  a coating layer  18  is provided on the reverse surface of the transparent base material opposite to the prism surface  16,  spherical beads  20  are arranged projecting from the surface of the coating layer  18  by 1 to 10 μm in height, and the coating layer  18  is brought into contact with the flat and smooth surface  22 A of the light-transmissive material  22  through the spherical beads  20  which are put between them. The spherical beads are 1 μm or less in half bandwidth of the distribution of particle diameters and are made uniform in height projecting from the coating layer  18.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an optical sheet and an opticalsheet lamination (“lamination” includes stacking or putting on in notcontact with another) composed of a prism sheet, a lens sheet and/or anoptical diffusing sheet suitable for use in a back light surface lightsource used in illuminating from the back a light-transmissive typedisplay panel of a light-transmissive type liquid crystal displayapparatus, an advertising board or the like, and a surface light sourcedevice and a light-transmissive type display apparatus using the sameoptical sheet or optical sheet lamination.

[0003] 2. Prior Art

[0004] In a liquid crystal display apparatus in recent years, accordingto necessity of reducing of its power consumption and making it thin andlight in shape and weight, a surface light source for illuminating theliquid crystal display apparatus from the back has been naturallyrequired also to be made thin and light in shape and weight and has beenreduced in power consumption in its light source by effectivelyutilizing light from the light source for reduction of powerconsumption.

[0005] In response to such requirement, such techniques for directinglight from a surface light source in a particular direction (in thenormal direction to a light outputting surface in many cases) have beenproposed as disclosed in Japanese laid-open publication Tokkaisho No.60-70601, Tokkaihei No. 2-84618, Jikkaihei No. 3-69184, Tokkaihei No.7-191319 and the like.

[0006] As a surface light source device used in a light-transmissivetype liquid crystal display apparatus and the like there are lightsource devices of an edge-light type and of a direct back light type.

[0007] A surface light source device of an edge-light type, as disclosedin a Japanese laid-open publication Tokkaihei No. 3-5725, has alight-source light inputted into it usually through one side end surfaceof a plate-shaped light guide means of a transparent acryl resin or thelike, leads the light to an light outputting surface which is the othersurface of the light guide means, and therefrom outputs the light to theback surface of a liquid crystal panel or the like.

[0008] In such a case, in order to improve the efficiency of utilizinglight, an optical reflector plate or an optical reflector film is oftenprovided on the opposite surface of said light guide means to the lightoutputting surface and in order to make the output light uniform, alight diffusing sheet having a light diffusing function is oftenprovided at the light outputting surface side of the light guide means,as disclosed in a Japanese laid-open publication Jikkaihei No. 5-73602and the like, for example.

[0009] A surface light source device of a direct back light type, asdisclosed in a Japanese laid-open publication Jikkaihei No. 2-33001 forexample, generally reflects a light-source light onto the back surfaceof a liquid crystal panel or the like by means of a reflector plate anddiffuses its output light by means of a light diffusing sheet disposedat the light outputting surface side so that the shape of the lightsource cannot be identified by human eyes.

[0010] Some of such surface light source devices of an edge-light typeor a direct back light type as described above are provided with a prismsheet (prism film) or a lens sheet (lens film) which has an array ofplural unit prisms or plural unit lenses arranged on the obverse surfaceof the light-transmissive base material of it in order to output lightfrom a surface light source collectively in a particular direction, asdescribed above.

[0011] Various applications of such optical sheets have been proposed incombination of plural optical sheets and in direction of setting theside at which unit prisms or unit lenses are formed (prism side or lensside) with regard to the light source side.

[0012] In such an optical sheet as described above, the opposite surface(reverse surface) to the prism surface or lens surface is often formedinto a flat and smooth surface.

[0013] In an optical sheet as described above, a pattern where brightand dark parts are alternately repeated by light from a surface lightsource is observed in case of combination of a light guide means, adiffusing sheet, another optical sheet and the like, and a problem thatan image composed of pixels is disarranged has been caused by this incase that such an optical sheet is used in a liquid crystal displayapparatus, for example.

[0014] On the other hand, as disclosed in a Japanese laid-openpublication Tokkaihei No. 7-151909 for example, a method for solvingthis problem has been proposed on the assumption that said pattern ofrepeating bright and dark parts is caused by interference fringesgenerated by an outside light source between the prism surface of oneprism sheet and the flat and smooth surface of the other prism sheet incase of using two prism sheets, for example.

[0015] When we have checked this assumption, however, a pattern ofrepeating bright and dark parts has been observed in a surface lightsource device even in a darkroom where no light enters from any outsidelight source.

[0016] That is to say, we have confirmed that interference fringes aregenerated by a surface light source rather than an outside light sourceand further generated between the flat and smooth surface of a prismsheet and the flat and smooth face of a light guide plate or the flatand smooth surface of a diffusing plate or other prism sheets.

[0017] On the other hand, a method of forming minute rugged partssatisfying a particular condition on the flat and smooth surface of aprism sheet is also conceivable as disclosed in said Tokkaihei No.7-151909, but in this case, there is a problem that the primary functionof a prism sheet for improving the brightness by collecting light from asurface light source in a particular direction, for example, in thenormal direction to the light outputting surface is deteriorated.

[0018] As for the light outputting side, many existing prism sheets asdescribed above are made so as to cover defects (flaws, stains and thelike) of a prism sheet by laminating a light diffusing sheet on theprism surface side which is a light outputting surface and are somewhatweakened in directivity of their light outputting characteristics.

[0019] Such a prism sheet having a light diffusing sheet laminated on ithas a problem that a prism (or lens) part touching the light diffusingsheet is damaged by a rugged part on the surface of the light diffusingsheet and this flaw deteriorates a uniform and flat light-emitting stateas a whole.

[0020] On the other hand, although a method of forming the prism sheetside of a light diffusing sheet into a flat and smooth surface in thesame way as the light inputting surface of said prism sheet is alsoconceivable, such a method as this has not come to be in practical usesince there is a problem that interference fringes or moire patterns aregenerated between the flat and smooth surface of said light diffusingsheet and the flat and smooth surface of a light guide plate or the flatand smooth surface of a prism sheet.

SUMMARY OF THE INVENTION

[0021] The present invention has been performed in consideration of theabove-mentioned existing problems, and an object of the invention is toprovide an optical sheet and an optical sheet lamination (in the presentinvention, “lamination” includes stacking or putting on in not contactwith another) which are made so as to suppress deterioration inbrightness of the light outputting side and generation of interferencefringes and so as not to damage other prism sheets being in contact withthem, and a surface light source device and a light-transmissive typedisplay apparatus using the same optical sheet and optical sheetlamination.

[0022] The present invention attains the above-mentioned object by meansof an optical sheet which has one surface of its light-transmissive basematerial on which at least one of a group of plural unit prisms and agroup of plural unit lenses is arranged and the other surface of itcoated with a coating layer formed out of light-transmissive materials,wherein said coating layer is composed of a light-transmissive resin andlight-transmissive fine particles dispersed in this light-transmissiveresin, and at least part of said fine particles form a number of fineknoll-shaped projections of 1 to 10 μm in height projecting from saidsurface by being projected from the opposite surface of said coatinglayer to the light-transmissive base material.

[0023] The coating layer in said optical sheet may be 2 to 20 μm inthickness including said fine knoll-shaped projections.

[0024] The fine knoll-shaped projections in said optical sheet may bedisposed at random along said surface of said coating layer.

[0025] At least part of the fine particles in said optical sheet may becomposed of light-transmissive beads of 1 to 10 μm in particle diameter.

[0026] The fine particles in said optical sheet may be composed ofspherical beads of 1 μm or less in half bandwidth of the distribution ofparticle diameters.

[0027] The ratio of the refractive index of a material forming the fineparticles in said optical sheet to the refractive index of alight-transmissive resin of said coating layer may be 0.9 to 1.1.

[0028] The coating layer in said optical sheet may be formed by applyingand drying an ink to the reverse surface of said light-transmissive basematerial, said ink being obtained by mixing with each other saidlight-transmissive resin and said light-transmissive beads less inspecific gravity than this resin, and said fine knoll-shaped projectionsare formed by projecting said light-transmissive beads from saidink-coated film which has dried and contracted.

[0029] At least part of fine particles in said optical sheet may beformed out of light-transmissive beads, and said light-transmissivebeads are distributed unevenly more at the opposite surface side of saidcoating layer to the light-transmissive base material and projected fromsaid surface.

[0030] The coating layer in said optical sheet may be formed by applyingan ink obtained by mixing with each other said light-transmissive resinand said light-transmissive beads less in specific gravity than thisresin to the reverse surface of said light-transmissive base material soas to be pressed by gravity, and by hardening the ink after saidlight-transmissive beads come to be distributed unevenly more in thevicinity of the surface after the ink has been applied.

[0031] The present invention attains the above-mentioned object by meansof an optical sheet which has one surface of its light-transmissive basematerial on which at least one of a group of plural unit prisms and agroup of plural unit lenses is arranged and the other surface of itcoated with a coating layer formed out of light-transmissive materials,wherein said coating layer is composed of a light-transmissive resin andlight-transmissive beads which are dispersed in this light-transmissiveresin, 1 to 10 μm in particle diameter and 1 μm or less in halfbandwidth of the distribution of particle diameters, and at least partof said light-transmissive beads are projected from the opposite surfaceof said coating layer to the light-transmissive base material andthereby many fine knoll-shaped projections of 1 to 10 μm in heightprojecting from said surface are formed and said coating layer is formedto be 2 to 20 μm in thickness including said fine knoll-shapedprojections, and the ratio of the refractive index of a material formingsaid light-transmissive beads to the refractive index of thelight-transmissive resin in the coating layer is 0.9 to 1.1.

[0032] The light-transmissive beads in said optical sheet may bedistributed unevenly more at the opposite surface side of said coatinglayer to the light-transmissive base material and projected from saidsurface.

[0033] And the present invention attains the above-mentioned object bymeans of an optical sheet having a light-transmissive base materialhaving one surface having a light diffusing layer on it and the othersurface covered with a coating layer formed out of a light-transmissivematerial, said coating layer comprising light-transmissive sphericalbeads of 1 μm or less in half bandwidth of the distribution of particlediameters.

[0034] The light diffusing layer in said optical sheet may be formed soas to contain light-transmissive beads, and the average particlediameter of the light-transmissive spherical beads in this lightdiffusing layer may be made larger than the average particle diametercontained in said coating layer.

[0035] The spherical beads contained in the coating layer in saidoptical sheet may be 1 to 10 μm in particle diameter.

[0036] The present invention attains the said object by means of anoptical sheet lamination which is formed by laminating together pluraloptical sheets containing unit prisms or unit lenses, wherein eachoptical sheet has plural unit prisms or unit lenses arranged on onesurface of a light-transmissive base material and the other surfacebeing covered with a coating layer formed out of a light-transmissivematerial, said coating layer contains light-transmissive spherical beadsof 1 μm or less in half bandwidth of the distribution of particlediameters, and said coating layer in the laminated optical sheet is incontact with unit prisms or unit lenses of another optical sheetlaminated adjacently to it.

[0037] Moreover, the present invention attains the said object by meansof an optical sheet lamination which is formed by laminating togetherone or more optical sheets each of which has a light-transmissive basematerial having one surface having a light diffusing layer on it and theother surface covered with a coating layer formed out oflight-transmissive materials, said coating layer containinglight-transmissive spherical beads of 1 μm or less in half bandwidth ofthe distribution of particle diameters, and one or more optical sheetseach of which has plural unit prisms or plural unit lenses arranged onthe surface of a light-transmissive base material, wherein said coatinglayer in an laminated optical sheet is in contact with unit prisms orunit lenses of another optical sheet laminated adjacently to it.

[0038] The vertical angle of the tops of said prisms or lenses of theoptical sheets being in contact with the coating layer of anotheroptical sheet may be as sharp as 100° or less.

[0039] And the present invention attains the said object by means of asurface light source device composed of a light source for outputtinglight from its light outputting surface and an optical sheet providedadjacently to said light outputting surface, said optical sheet havingone surface of a light-transmissive base material on which at least oneof a group of plural unit prisms and a group of plural unit lenses isarranged and the other surface being covered with a coating layer formedout of light-transmissive materials, wherein said coating layer iscomposed of a light-transmissive resin and light-transmissive fineparticles dispersed in this light-transmissive resin, and at least partof said fine particles are formed into many fine knoll-shapedprojections of 1 to 10 μm in height projecting from said surface bybeing projected from the opposite surface of said coating layer to thelight-transmissive base material.

[0040] The coating layer in said optical sheet may be 2 to 20 μm inthickness including said fine knoll-shaped projections.

[0041] At least part of the fine particles in said surface light sourcedevice may be light-transmissive beads of 1 to 10 μm in particlediameter.

[0042] Said fine particles in the coating layer of said surface lightsource device may be spherical beads of 1 μm or less in half bandwidthof the distribution of particle diameters.

[0043] The ratio of the refractive index of a material forming the fineparticles in said surface light source device to the refractive index ofa light-transmissive resin of said coating layer may be 0.9 to 1.1.

[0044] At least one lens sheet which has one surface of alight-transmissive base material in said surface light source on whichat least one of a group of plural unit prisms and a group of plural unitlenses arranged, and the other surface being made flat and smoothwithout raggedness by being covered with a coating layer formed out of alight-transmissive material is put between said optical sheet and saidlight outputting surface.

[0045] A light source in said surface light source device may becomposed of a light guide means which is a plate-shaped member one ofwhose surfaces is said light outputting surface and which outputs alight introduced through at least one side end surface from said lightoutputting surface, and a light generating source for inputting lightinto said light guide means through at least said one side end surfaceof said light guide means.

[0046] A light diffusing sheet may be disposed on the light outputtingsurface of the light source in said surface light source device and thelight outputted through said light diffusing sheet from said lightoutputting surface may be inputted from said coating layer side.

[0047] At least part of said fine particles in said surface light sourcedevice may be formed out of light-transmissive beads, and saidlight-transmissive beads may be distributed unevenly more at theopposite surface side of said coating layer to the light-transmissivebase material and may be formed into many fine knoll-shaped projectionsby being projected from said surface.

[0048] The present invention attains the said object by means of asurface light source device composed of a light source for outputtinglight from its light outputting surface and an optical sheet providedadjacently to said light outputting surface, said optical sheet havingone surface of a light-transmissive base material on which at least oneof a group of plural unit prisms and a group of plural unit lenses isarranged and the other surface being covered with a coating layer formedout of light-transmissive materials, wherein said coating layercomprises light-transmissive spherical beads of 1 μm or less in halfbandwidth of the distribution of particle diameters and the lightoutputted from said light outputting surface is inputted from saidcoating layer side.

[0049] Said light diffusing layer in said surface light source devicemay comprise light-transmissive spherical beads, and the averageparticle diameter of the light-transmissive spherical beads in saidlight diffusing layer may be larger than the average particle diameterof the spherical beads contained in said coating layer.

[0050] The spherical beads contained in the coating layer in saidsurface light source device may be 1 to 10 μm in particle diameter.

[0051] The present invention attains the said object by means of asurface light source device composed of a light source for outputtinglight from its light outputting surface and an optical sheet providedadjacently to said light outputting surface, said optical sheet havingone surface of a light-transmissive base material on which at least oneof a group of plural unit prisms and a group of plural unit lenses isarranged and the other surface being covered with a coating layer formedout of light-transmissive materials, wherein said coating layer containsa light-transmissive resin and light-transmissive beads, dispersed inthis light-transmissive resin, of 1 to 10 μm in particle diameter and 1μm or less in half bandwidth of the distribution of particle diameters,and at least part of said light-transmissive beads are formed into manyfine knoll-shaped projections of 1 to 10 μm in height projecting fromthe opposite surface of said coating layer to the light-transmissivebase material by being projected from said opposite surface, and saidcoating layer is 2 to 20 μm in thickness including said fineknoll-shaped projections, and the ratio of the refractive index of amaterial forming said light-transmissive beads to the refractive indexof the light-transmissive resin in the coating layer is 0.9 to 1.1.

[0052] The light-transmissive beads in said surface light source devicemay be distributed unevenly more at the opposite surface side of saidcoating layer to the light-transmissive base material and projected fromsaid surface.

[0053] The vertical angle of the tops of said prisms or lenses of theoptical sheets being in contact with the coating layer of anotheroptical sheet may be as sharp as 100° or less.

[0054] The present invention attains the said object by means of alight-transmissive type display apparatus composed of a flatlight-transmissive display means and a surface light source device whichis disposed at the back of said light-transmissive display means andirradiates said light-transmissive display means from the back with itsoutput light, wherein said surface light source device is composed of alight source for outputting light from its light outputting surface andan optical sheet provided adjacently to said light outputting surface,said optical sheet having one surface of a light-transmissive basematerial on which at least one of a group of plural unit prisms and agroup of plural unit lenses is arranged and the other surface beingcovered with a coating layer formed out of light-transmissive materials,and light-transmissive fine particles different from a material for thecoating layer are disposed on the opposite surface of said coating layerto the light-transmissive base material and thereby many fineknoll-shaped projections of 1 to 10 μm in height projecting from saidsurface are formed, and the light outputted from said light outputtingsurface is inputted from said coating layer side.

[0055] Said coating layer of the optical sheet in saidlight-transmissive type display apparatus may be 2 to 20 μm in thicknessincluding said fine knoll-shaped projections.

[0056] At least part of said fine particles of the optical sheet in saidlight-transmissive type display apparatus may be light-transmissivebeads of 1 to 10 μm in particle diameter.

[0057] Said fine particles of the coating layer of the optical sheet insaid light-transmissive type display apparatus may be spherical beads of1 μm or less in half bandwidth of the distribution of particlediameters.

[0058] The ratio of the refractive index of a material forming said fineparticles of the optical sheet in said light-transmissive type displayapparatus to the refractive index of the light-transmissive resin of thecoating layer may be is 0.9 to 1.1.

[0059] At least one lens sheet which has one surface of alight-transmissive base material in said light-transmissive displayapparatus on which at least one of a group of plural unit prisms and agroup of plural unit lenses is arranged and the other surface being madeflat and smooth without raggedness by being covered with a coating layerof a light-transmissive material may be put between said optical sheetand said light outputting surface in said surface light source device.

[0060] Said light source of said surface light source device in saidlight-transmissive type display apparatus may be composed of a lightguide means which is a plate-shaped member, formed out of alight-transmissive material, having one surface of it as said lightoutputting surface and outputs a light inputted from at least one sideend surface through said light outputting surface, and a lightgenerating source for inputting light from at least said one side endsurface of said light guide means into it.

[0061] A light diffusing sheet may be disposed on the light outputtingsurface of said light source in said light-transmissive type displayapparatus, and a light outputted through said light diffusing sheet fromsaid light outputting surface may be inputted from said coating layerside.

[0062] At least part of said fine particles of the optical sheet in saidlight-transmissive type display apparatus may be formed out oflight-transmissive beads, and said light-transmissive beads may bedistributed unevenly more at the opposite surface side of said coatinglayer to the light-transmissive base material, and formed into said manyfine knoll-shaped projections by being projected from said surface.

[0063] The present invention attains the said object by means of alight-transmissive type display apparatus provided with a flatlight-transmissive display means and a surface light source device whichis disposed at the back of this light-transmissive display means andirradiates said light-transmissive display means from the back with itsoutput light, wherein said surface light source device is composed of alight source for outputting light from its light outputting surface andan optical sheet provided adjacently to said light outputting surface,wherein said optical sheet has one surface of a light-transmissive basematerial on which a light diffusing sheet is provided and the othersurface being covered with a coating layer of light-transmissivematerials, and said coating layer contains light-transmissive sphericalbeads of 1 μm or less in half bandwidth of the distribution of particlediameters, and at least part of these spherical beads are projected fromthe opposite surface of said coating layer to the light-transmissivebase material and are formed into many fine knoll-shaped projections of1 to 10 μm in height projecting from said surface, and the lightoutputted from said light outputting surface is inputted from saidcoating layer side.

[0064] Said light diffusing layer of the optical sheet in saidlight-transmissive type display apparatus may contain light-transmissivespherical beads, and the average particle diameter of thelight-transmissive spherical beads in said light diffusing layer may bemade larger than the average particle diameter of the spherical beadscontained in said coating layer.

[0065] The spherical beads contained in said coating layer of theoptical sheet in said light-transmissive type display apparatus may be 1to 10 μm in particle diameter.

[0066] The present invention attains the said object by means of alight-transmissive type display apparatus provided with a flatlight-transmissive display means and a surface light source device whichis disposed at the back of this flat light-transmissive display meansand irradiates said light-transmissive display means from the back withits output light, wherein said surface light source device is composedof a light source for outputting light from its light outputting surfaceand an optical sheet provided adjacently to said light outputtingsurface, said optical sheet has one surface of a light-transmissive basematerial on which at least one of a group of plural unit prisms and agroup of plural unit lenses is arranged and the other surface beingcovered with a coating layer formed out of light-transmissive materials,said coating layer is composed of a light-transmissive resin andlight-transmissive beads which are dispersed in this light-transmissiveresin and are 1 to 10 μm in particle diameter and 1 μm or less in halfbandwidth of the distribution of particle diameters, and at least partof said light-transmissive beads are formed into many fine knoll-shapedprojections of 1 to 10 μm in height projecting from the opposite surfaceof said coating layer to the light-transmissive base material by beingprojected from said surface, and said coating layer is 2 to 20 μm inthickness including said fine knoll-shaped projections, and the ratio ofthe refractive index of a material forming said light-transmissive beadsto the refractive index of the light-transmissive resin in said coatinglayer is 0.9 to 1.1.

[0067] Said light-transmissive beads of the optical sheet in saidlight-transmissive type display apparatus may be distributed unevenlymore at the opposite surface side of said coating layer to thelight-transmissive base material and may be projected from said surface.

[0068] According to the present invention, since many fine knoll-shapedprojections of 1 to 10 μm in height are provided on a coating layercovering the reverse surface opposite to the lens surface of a lenssheet, a gap of 1 to 10 μm is formed between said reverse surface andthe flat and smooth surface of a light guide plate, a light diffusingplate, another lens sheet or the like disposed adjacently to saidreverse surface, and thereby the distance between said reverse surfaceand the flat and smooth surface of a light guide plate or the like iskept so that no interference is generated between an advancing light anda reflected light and thus generation of interference fringes orNewton's rings can be prevented.

[0069] The vertical angle of the tops of said prisms or lenses of theoptical sheets being in contact with the coating layer of anotheroptical sheet may be as sharp as 100° or less.

[0070] According to the present invention, since light-transmissivebeads are distributed unevenly more at the vicinity of the surface of acoating layer in case of providing many fine knoll-shaped projections of1 to 10 μm in height by distributing the light-transmissive beads in thecoating layer covering the reverse surface opposite to the prism surfaceof a prism sheet, the invention is economical and efficient thanks todoing with a small amount of beads to be used, and can suppress aphenomenon of deteriorating the primary function of a prism sheet ofimproving the brightness of a display screen by collecting light in thedirection perpendicular to the light outputting surface which phenomenoncomes into question in case of forming a light diffusing layer on thereverse surface opposite to its prism surface of a prism sheet. Sincethe coating layer is hardened and formed in a state where an inkcontaining light-transmissive beads smaller in specific gravity than thelight-transmissive resin is applied to the light-transmissive basematerial and the light-transmissive beads have come up to the surface ofthe ink thanks to the difference in specific gravity between them, it ispossible to easily and surely distribute the light-transmissive beadsunevenly more in the vicinity of the surface of the coating layer.

[0071] According to the present invention, since spherical beads arecontained in a coating layer which covers the reverse surface oppositeto the lens surface or the prism surface of an optical sheet or thereverse surface of an optical sheet having a light diffusing layer onits obverse surface, a small gap is formed between said reverse surfaceand the flat and smooth surface of a light guide plate, a lightdiffusing plate, another prism sheet or the like disposed adjacently tosaid reverse surface, and a light diffusing effect by the sphericalbeads prevents interference between an advancing light and a reflectedlight due to a distance between said reverse surface and the flat andsmooth surface of a light guide plate or the like and preventsgeneration of interference fringes or Newton's rings. And since thespherical beads contained in the coating layer are 1 μm or less in halfbandwidth of the distribution of particle diameters, the projectionsfrom the reverse surface of an optical sheet vary a little in height andare uniformly in contact with another optical sheet such as a prismsheet or the like, and therefore a trouble is prevented that a prism orthe like of another optical sheet is broken by a concentrated loadcaused by a greatly projected spherical bead.

[0072] The vertical angle of the tops of said prisms or lenses of theoptical sheets being in contact with the coating layer of anotheroptical sheet may be as sharp as 1000 or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073]FIG. 1 is a perspective view magnifying part of an optical sheethaving a prism surface according to embodiment of the present invention.

[0074]FIG. 2 is a sectional view further magnifying part of the sameoptical sheet.

[0075]FIGS. 3a and 3 b are sectional views showing a process of forminga coating layer in the same optical sheet.

[0076]FIGS. 4a and 4 b are perspective views showing a second and afourth example of embodiment of a prism surface or a lens surface of theoptical sheet.

[0077]FIGS. 5a and 5 b are perspective views showing a fifth and a sixthexample of the same.

[0078]FIG. 6 is a perspective view showing a first example of embodimentof an optical sheet lamination.

[0079]FIG. 7 is a perspective view showing a second example of the sameembodiment.

[0080]FIG. 8 is a sectional view magnifying part of an optical sheet asa light diffusing sheet according to the second example of embodiment ofthe present invention.

[0081]FIG. 9 is a sectional view showing a process of forming a coatinglayer of the same optical sheet.

[0082]FIG. 10 is a perspective view showing a first example ofembodiment of an optical sheet lamination using the same optical sheet.

[0083]FIG. 11 is a sectional view magnifying part of an optical sheetaccording to a third example of embodiment of the present invention.

[0084]FIGS. 12a and 12 b are sectional views showing a process offorming a coating layer of the same optical sheet.

[0085]FIG. 13 is a perspective view showing the main part of a surfacelight source device using an optical sheet having a prism surfaceaccording to embodiment of the invention.

[0086]FIG. 14 is a perspective view showing a second example ofembodiment of the same surface light source device.

[0087]FIG. 15 is a sectional view roughly showing a third example ofembodiment of the same surface light source device.

[0088]FIG. 16 is a sectional view roughly showing a fourth example ofthe same embodiment.

[0089]FIG. 17 is a sectional view roughly showing a fifth example of thesame embodiment.

[0090]FIG. 18 is a perspective view showing the main part of a sixthexample of the same embodiment.

[0091]FIG. 19 is a perspective view showing the main part of a seventhexample of the same embodiment.

[0092]FIG. 20 is a perspective view showing the main part of an eighthexample of the same embodiment.

[0093]FIG. 21 is a perspective view showing the main part of a ninthexample of the same embodiment.

[0094]FIG. 22 is a side view roughly showing a liquid crystal displayapparatus according to an embodiment of the invention.

[0095]FIG. 23 is a perspective view showing the main part of a surfacelight source device according to an embodiment using an optical sheetwhich is a light diffusing sheet of the present invention.

[0096]FIG. 24 is a perspective view showing a second example ofembodiment of the surface light source device.

[0097]FIG. 25 is a sectional view roughly showing a third example ofembodiment of the same surface light source device.

[0098]FIG. 26 is a sectional view roughly showing a fourth example ofembodiment of the same embodiment.

[0099]FIG. 27 is a perspective view showing the main part of a fifthexample of the same embodiment.

[0100]FIG. 28 is a perspective view showing the main part of a sixthexample of the same embodiment.

[0101]FIG. 29 is a perspective view showing the main part of a seventhexample of the same embodiment.

[0102]FIG. 30 is a perspective view showing the main part of an eighthexample of the same embodiment.

[0103]FIG. 31 is a side view roughly showing a liquid crystal displayapparatus according to an embodiment of the invention.

[0104]FIGS. 32a and 32 b are magnified sectional views comparativelyshowing an optical sheet coated with spherical beads of the presentinvention and an optical sheet coated with spherical beads varyinggreatly in particle diameter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0105] Embodiments of the present invention are described in detail withreference to the drawings in the following.

[0106] As shown in FIGS. 1 and 2, an optical sheet 10 according to thepresent invention forms a prism surface 16 by arranging many unit prisms14 each of which is in the shape of a triangular prism on one surface(the upper surface in FIGS. 1 and 2) of a transparent base materialsheet 12 adjacently to one another in a one-dimensional direction sothat their ridge-lines 14A are in parallel with one another, and acoating layer 18 is provided on the reverse surface opposite to thisprism surface 16 and moreover this coating layer 18 contains sphericalbeads 20 formed out of a light-transmissive material which are 1 to 10μm in particle diameter and 1 μm or less in half bandwidth of thedistribution of particle diameters.

[0107] And part of the spherical beads 20 distributed two-dimensionallyat random on the surface of said coating layer 18 are projected fromsaid surface and formed into many knoll-shaped projections 20A as shownin FIG. 3(B).

[0108] In case of disposing said optical sheet 10 so as to bring itscoating layer 18 side into contact with a flat and smooth surface 22A ofanother light-transmissive material 22, for example, a light guideplate, a light diffusing sheet or another prism sheet, in the prior artas described above, interference fringes have been generated by asurface light-source light from said light guide plate or the like, butin an optical sheet 10 of the present invention as shown in FIG. 2, theflat and smooth surface 22A of a light-transmissive material 22 of alight guide means or the like comes into contact with the sphericalbeads 20 projecting from the surface of the coating layer 18, a gap 24of 1 to 10 μm or so is generated without fail between said flat andsmooth surface 22A and the surface of the coating layer 18.

[0109] Accordingly, even when light is inputted through the oppositeside of the light-transmissive material 22 to the flat and smoothsurface 22A (through the lower side in FIG. 2), the gap 24 preventsgeneration of interference fringes in cooperation with a light diffusingeffect of the spherical beads.

[0110] Since the spherical beads 20 are made so as to be 1 μm or less inhalf bandwidth of the distribution of particle diameters, variation inheight of the projections of the spherical beads 20 from the surface ofthe coating layer 18 becomes 1 μm or less.

[0111] Accordingly, when said spherical beads 20 come into contact withthe tops of prism parts on another prism sheet or the flat and smoothsurface of another light-transmissive material, their contact state isuniform and therefore there is not a trouble that a concentrated load iscaused by contact with a greatly projected spherical bead and a prismpart of a prism sheet or the like is prevented from being damaged, evenif vertical angle of the tops of the prism parts of the another prismsheet is as sharp as 100° or less.

[0112] Hereupon, the reason why the projections of said spherical beads20 are made 1 μm or more in height from the surface of the coating layer18 is that a height of less than 1 μm causes a problem that said gap 24being close to the wavelength of a surface light-source light (visiblelight) makes color appear, a problem that it becomes difficult tomass-produce light-transmissive beads (acryl beads for example) as amaterial for the spherical beads 20, and a problem that such fine beadsare difficult to be dispersed in a binder (described later) forming thecoating layer 18. Furthermore, the reason is also to avoid a problemthat a uniform brightness in the surface cannot be kept due to a factthat a light from the light-transmissive material comes directly intothe coating layer 18 as an evanescent wave.

[0113] The reason why the spherical beads 20 are 10 μm or less inparticle diameter is that the gap 24 being larger than 10 μm in particlediameter deteriorates greatly an effect of collecting light from thesurface light source in a particular direction, for example, the normaldirection to the light outputting surface at the prism surface 16 side.

[0114] In case of providing the spherical beads 20 on the coating layer18, light-transmissive beads or the like forming said spherical beads 20are mixed with a binder and then applied to the reverse surface of theoptical sheet 10 (described later), and in this case projections of thespherical beads 20 vary in height, and the height of the projections isreferred to as the 10-point average roughness Rz according to JIS B0601of the Japanese Industrial Standards.

[0115] As said spherical beads 20 are not arranged periodically buttwo-dimensionally at random on the surface of the coating layer 18.

[0116] If the spherical beads 20 are arranged periodically on thecoating layer 18 and this arrangement period nearly coincides with theperiod in arrangement of the unit prisms 14, moire fringes appear.

[0117] For example, in case of providing such an optical sheet asdescribed above at the light outputting surface side of the back lightof a color liquid crystal display apparatus, when the spherical beads 20are periodically arranged there is a possibility that moire fringes arecaused by a fact that the period in arrangement of the spherical beads20 nearly coincides with the period in arrangement of pixels of thecolor liquid crystal display apparatus.

[0118] In the optical sheet 10 according to the present invention, sincethe spherical beads 20 are disposed two-dimensionally at random, suchmoire fringes as described above are not generated.

[0119] As transparent materials for a transparent base sheet 12, unitprisms 14 and spherical beads 20 forming said optical sheet, materialsgood in transparency are used, said materials being selected out ofresins obtained by hardening ionizing-radiation setting resins composedof such polyester resins as polyethylene terephtalate, polybutyleneterephtalate and the like, such acryl resins as polymethyl methacrylateand the like, such thermoplastic resins as polycarbonate resin,polystyrene resin, polymethyl pentene resin and the like, and sucholigomer and/or monomer resins of acrylate system as polyester acrylate,uretane acrylate, epoxy acrylate and the like with such anelectromagnetic radiation as ultraviolet rays, electron rays or thelike.

[0120] In case of using such a resin, a resin of 1.4 to 1.6 or so inrefractive index is usually used. In addition to such resins, glass,ceramic and the like which are transparent may be used.

[0121] Such a coating layer 18 containing the spherical beads 20 asdescribed above is formed by applying a coating material obtained bydispersing the spherical beads 20 in a transparent binder to a sheet bymeans of spray coating, roll coating or the like and making at leastpart of the spherical beads 20 project from the surface of the coatedfilm.

[0122] In this case, as shown in FIG. 3(A), the spherical beads 20 aresubmerged under the surface of the coating layer just formed by applyinga coating material having the spherical beads 20 dispersed in atransparent binder to a sheet, but part of the spherical beads 20 areprojected from the surface of the coating layer 18 as the coated film isdried and contracted.

[0123] Hereupon, as a material for the spherical beads 20, beads of 1 to10 μm in diameter are used, said beads being formed out of methylpolymethacrylate (acryl) system, butyl polymethacrylate system,polycarbonate system, polyuretane system, calcium carbonate system,silica system and the like. The diameter of the spherical beads 20 meansthe average diameter of particles of 1 μm or more.

[0124] As a binder resin for forming said coating layer 18, such atransparent material as acryl, polystyrene, polyester, vinyl polymer orthe like is used, and the ratio of the refractive index of a materialfor the spherical beads 20 to the refractive index of a binder resin ispreferably in a range from 0.9 to 1.1, and furthermore the density oflight-transmissive fine particles is preferably 2 to 15% of the binderresin.

[0125] A range of said refractive index ratio of 0.9 to 1.1 isdetermined by the reason that a refractive index ratio out of said rangedeteriorates remarkably the primary function of an optical sheet havinga prism surface, said function collecting a surface light-source lightinputted through the surface of the coating layer 18 in a particulardirection, for example, the normal direction to the light outputtingsurface to improve the brightness.

[0126] The thickness of said coating layer 18 is preferably in a rangefrom 1 to 20 μm except the projection height of the spherical beads 20.

[0127] The reason is that a coating layer 18 being less than 1 μm inthickness makes it impossible to fix the spherical beads 20 on thereverse surface of the transparent base sheet 12, and the coating layer18 being 20 μm or more in thickness is reduced in optical transmissivityand deteriorates remarkably the primary function of an optical sheethaving a prism surface for improving the brightness.

[0128] As for a method for manufacturing said optical sheet 10, anoptical sheet of a single-layer structure (an intermediate sheet beforecoating) can be manufactured by a thermal press method of thermoplasticresins, an injection molding method, a mold-casting method ofultraviolet-setting or thermosetting resins as disclosed in a Japaneselaid-open publication Tokkaisho No. 56-157310, for example.

[0129] And as another method for manufacturing such an intermediatesheet as described above, there is a method which, as disclosed in aJapanese laid-open publication Tokkaihei No. 5-1699015 for example,fills an intaglio roll having hollow parts (exactly, concave and convexparts) in the reverse shape to the shape of a desired lens array with anionizing-radiation setting resin liquid, puts a transparent base sheet12 on this roll, irradiates the transparent base sheet with an ionizingradiation such as ultraviolet rays, electron rays and the like as theyare to harden the ionizing-radiation setting resin liquid, and thenexfoliates the transparent base sheet together with the hardenedionizing-radiation setting resin from the intaglio roll and therebyforms a lens array in a desired shape on the transparent base sheet byhardening the ionizing-radiation setting resin liquid. Hereupon, thetotal thickness of said optical sheet 10 is usually about 20 to 1000 μm.

[0130] In the above-mentioned optical sheet 10, although the prismsurface 16 is formed by arranging plural unit prisms 14 each of which isin the shape of a triangular prism in parallel with one another, thepresent invention is not limited to this but can do with an opticalsheet having pillar-shaped unit prisms arranged adjacently to oneanother so that the axes of them are in parallel with one another in aone-dimensional direction, like an optical sheet 10A provided with unitprisms 15A each of which is in the shape of a semicircular cylinder asshown in FIG. 4(A), an optical sheet 10B provided with unit prisms 15Bwhich show a sine curve in cross-sectional view as shown in FIG. 4(B),an optical sheet 10E provided with unit prisms 15E which show a sinecurve and a V shape in cross-sectional view, respectively, in the upperhalf part (mount part) and the lower half part (valley part) as shown inFIG. 4(C), and an optical sheet 10C provided with unit prisms 15C in theshape of trapezoids as shown in FIG. 5(A).

[0131] The section of a unit prism is not limited to the shape of asemicircle or a sine curve, but may be in the shape of a chaoid, aRankine's ovoid, a cycloid, an involute, and a polygon other than atriangle.

[0132] And as shown in FIG. 5(B), said optical sheet may be an opticalsheet 10D provided with a so-called compound-eye (fly-eye) lens and thelike where unit prisms 15D each of which is a semisphere andindependently projected are arranged in two-dimensional directions. Theunit prism may be in the shape of a pyramid.

[0133] Furthermore, an optical sheet of the invention may be improved indirectivity of its output light by being used as a sheet laminationobtained by laminating plural sheets on one another as shown in FIG. 6or 7.

[0134] An optical sheet lamination 26 shown in FIG. 6 is obtained bylaminating two optical sheets 10 on each other, where the upper opticalsheet 10 and the lower optical sheet 10 are disposed so that the coatinglayer 18 on the lower surface of the upper optical sheet 10 comes intocontact with the prism surface 16 of the upper surface of the loweroptical sheet 10. That is to say, the ridge-line 14A of each unit prism14 of the lower optical sheet 10 is in contact with the coating layer 18of the upper optical sheet 10.

[0135] The upper and lower optical sheets 10 are arranged so that theridge-lines 14A of the unit prisms 14 of the upper optical sheet andthose of the lower optical sheet are perpendicular to each other in aplan view of them.

[0136] In an optical sheet lamination 28 of FIG. 7, two optical sheets10 are arranged so that both of the prism surfaces 16 of them arebrought to the light receiving side by putting upside down each of thetwo optical sheets reversely to FIG. 6.

[0137] A second embodiment of the invention is described in detail withreference to the drawings in the following. In the second embodiment,the same parts as said optical sheet shown in FIGS. 1 and 2 are giventhe same symbols and description for them is omitted.

[0138] As shown in FIGS. 8 and 9, an optical sheet 30 according to thesecond example of embodiment of the invention is provided with atransparent base sheet 12, wherein one surface (the upper surface inFIGS. 8 and 9) of it is provided with a light diffusing layer 32 and theother surface opposite to this light diffusing layer 32 is provided witha coating layer 18, and spherical beads 20, formed out of alight-transmissive material, being 1 to 10 μm in particle diameter and 1μm or less in half bandwidth of the distribution of particle diametersare contained in this coating layer 18.

[0139] The spherical beads 20 are distributed two-dimensionally atrandom on the surface of said coating layer 18.

[0140] In case of disposing said optical sheet 30 so that its coatinglayer 18 side comes into contact with another light-transmissivematerial, for example, into contact with the prism surface of a prismsheet 36 having unit prisms 34 in the shape of a triangular prism asshown in FIG. 10, in the prior art as described above, a problem hasappeared that a prism part (or lens part) being in contact with a lightdiffusing sheet is damaged by a rugged portion on the surface of thelight diffusing sheet and thereby a uniform surface light emitting stateas a whole is deteriorated, but since the spherical beads 20 are 1 μm orless in half bandwidth of the distribution of particle diameters asdescribed above, variation in height of the spherical beads 20projecting from the surface of the coating layer 18 becomes 1 μm orless. Therefore, since said spherical beads 20 come uniformly in contactwith the tops of the prism parts on another prism sheet or the flat andsmooth surface of another light-transmissive material, a concentratedload caused by contact with a spherical bead greatly projected is notgenerated and a prism part or the like of the prism sheet is preventedfrom damage, even if the vertical angle θ of the tops of the prisms 34on another prism sheet 36 is as sharp as 100° or less.

[0141] The light diffusing layer 32 of said optical sheet 30 is enoughif it has a function of diffusing light, and is formed out of a coatinglayer of a light-transmissive material, for example, havinglight-transmissive spherical beads of 1 to 30 μm in particular diameter.

[0142] In this case, in order to increase an effect of improving thebrightness in the normal direction to the sheet as a light diffusingsheet, the average particle diameter of the light-transmissive sphericalbeads 20 in the light diffusing layer 32 needs to be made greater thanthe average particle diameter of the light-transmissive spherical beads20 in the coating layer 18.

[0143] Hereupon, although the half bandwidth of the distribution ofparticle diameters of the light-transmissive spherical beads in saidlight diffusing layer 32 is not limited in particular, in case thatanother optical material coming in contact with this light diffusinglayer 32 is damageable, said half bandwidth is preferably 1 μm or lessin the same way as the half bandwidth of the light-transmissivespherical beads in said coating layer 18.

[0144] Since said transparent base sheet 12, a coating layer 18, amaterial for spherical beads 20, characteristics of them and the likeare the same as the first example of said embodiment, description ofthem is omitted.

[0145] Although said optical sheet 30 is laminated on a prism sheet 36having unit prisms 34 each of which is in the shape of a triangularprism as shown in FIG. 10, the present invention is not limited to thisbut can do with a prism sheet in another shape, for example, a prismsheet provided with unit prisms as shown in FIGS. 4 and 5.

[0146] And said prism sheet may be formed into a lamination havingplural sheets put on one another as shown in FIGS. 6 and 7 to improvethe directivity of its output light. In this case, the upper and lowerprism sheets are preferably arranged so that the ridge-lines of the unitprisms of the upper optical sheet and those of the lower optical sheetare perpendicular to each other in a plan view of them.

[0147] And it is a matter of course that this optical sheet 30 can beused not only in case of being laminated on a prism sheet but also incase of being laminated on an optical material whose surface isdamageable.

[0148] A third example of embodiment of the present invention isdescribed in detail with reference to the drawings in the following.

[0149] As shown in FIG. 11, an optical sheet 40 according to theinvention is nearly the same as the optical sheet 10 of FIGS. 1 and 2,but is different from it in that the light-transmissive beads 20 aredistributed unevenly more on the surface of a coating layer 42.

[0150] Said coating layer 18 is formed by applying a coating material(ink) obtained by dispersing the light-transmissive beads 20 in alight-transmissive resin (binder) to a sheet by means of spray coating,roll coating or the like and making at least part of thelight-transmissive beads 20 project from the surface of the coated filmof the coating layer 42 to form fine knoll-shaped projections.

[0151] The light-transmissive beads 20 forming part of said coatingmaterial (ink) are selected so that its specific gravity is smaller thanthe specific gravity of said light-transmissive resin to be formed intoa binder.

[0152] Said coating material is applied so that the coated film ispressed by gravity to the reverse surface of the transparent base sheet12. For example, as shown in FIG. 12, said coating material is appliedto the upper surface of the transparent base sheet 12 in a state wherethe reverse surface of it faces upward, reversely to the state of FIG.11.

[0153] When the coating material has been applied in such a way, thelight-transmissive beads are distributed in the coated film in a liquidstate uniformly in the direction of its thickness as shown in FIG.12(A), but with the lapse of time (after 3 to 60 seconds) thelight-transmissive beads come up thanks to a specific gravity differenceand come together (are distributed unevenly) to the surface of thecoating layer 42 as shown in FIG. 12(B) and part of them project fromthe surface to be formed into fine knoll-shaped projections.

[0154] In this state the coating layer 42 is successfully hardened by ahardening means such as ultraviolet rays, electron rays, radioactiverays or the like suitable for the light-transmissive resin.

[0155] Even in case that the ink is a thermosetting ink containing agreat amount of such a solvent smaller in specific gravity than thelight-transmissive beads as toluene, methyl-ethyl ketone (MEK) or thelike, it is an essential condition of the present invention that thelight-transmissive beads are smaller in specific gravity than alight-transmissive resin (binder) including the solvent to volatilize atthe time of drying.

[0156] In case of a thermosetting ink, a mixture of liquid substances (atransmissive resin+a solvent) other than the light-transmissive beads 20is often smaller in specific gravity than the light-transmissive beads20; and in such a case, immediately after the coating layer 42 has beenjust formed by applying the ink to the opposite surface of thelight-transmissive base sheet to the gravity, the light-transmissivebeads 20 are uniformly distributed in the light-transmissive resin(binder), as shown in FIG. 12(A), and since the solvent volatilizes in adrying process after a coating process, namely, since a solventcomponent of said mixture (transmissive resin+solvent) volatilizes withthe lapse of time (usually 3 to 300 seconds), thanks to a fact that thespecific gravity of the light-transmissive beads 20 is smaller than thespecific gravity of the light-transmissive resin, part oflight-transmissive beads 20 are projected from the surface of thecoating layer 18 and thereby fine knoll-shaped projections are formed,as shown in FIG. 12(B).

[0157] Next, a surface light source device 50 according to an embodimentof the present invention is described with reference to FIG. 13 in thefollowing.

[0158] The surface light source device 50 is provided with the opticalsheet 10 shown in FIG. 1 at the light outputting surface side, andcomprises a light guidee means 52 which is in the shape of a plateformed out of a light-transmissive material and outputs a lightintroduced through the left side end surface 52A, as shown in FIG. 13,from the light outputting surface 52B at the upper side, a linear lightsource 54 which is disposed along and in parallel with said side endsurface 52A of the light guide means 52 and inputs a light through saidside end surface 52A into said light guide means 52, and an opticalreflector plate 56 which is disposed so as to cover the opposite surfaceof said light guide means 52 to the light outputting surface 52B and theother side end surfaces than the left side end surface 52A, and reflectsand returns lights outputted from these surfaces into the light guidemeans 52.

[0159] The coating layer 18 of said optical sheet 10 is disposed asbeing in contact with the light outputting surface 52B of said lightguide means 52. Said light guide means 52 is usually accommodated in anenclosure (not illustrated) having the light outputting surface 52B as awindow.

[0160] A material for said light guide means 52 is selected fromlight-transmissive materials similar to said optical sheet 10, andusually an acryl or carbonate resin is used. Said light guide means 52is usually about 1 to 10 mm in thickness, and is tapered so that it isthickest at the position of the side end surface 52A at the said linearlight source 54 side and becomes gradually thinner toward the oppositedirection from this position.

[0161] This light guide means 52 is additionally provided with a lightdiffusing function inside or on the surface of it in order to outputlight from the wide surface (light outputting surface 52B). Said linearlight source 54 is preferably a fluorescent lamp in a viewpoint ofgiving a uniform brightness on the light outputting surface 52B.

[0162] In this surface light source device 50, the light source forinputting light into the light guide 52 is not limited to a linear lightsource but may be a light source where such point light sources asincandescent light bulbs, light emitting diodes and the like arearranged in a line. And a plurality of small-sized flat fluorescentlamps may be arranged along the side end surface 52A.

[0163] In the surface light source device 50 shown in FIG. 13, since theoptical sheet 10 is brought into contact with the light outputtingsurface 52B of the light guide means 52 through the spherical beadsprojecting from the coating layer 18 and being put between them, it isprevented that interference fringes are generated between the surface ofthe coating layer 18 and the light outputting surface 52B. Accordingly,it is possible to form a good light emitting surface as a surface lightsource for a light-transmissive type liquid crystal display apparatus orthe like. And the spherical beads 20 hardly damage the light outputtingsurface 52B of the light guide means 52.

[0164] For example, the light guide means 52 may be in the shape of aplate uniform in thickness and be provided with a linear light sourcealso at the side end surface side opposite to said side end surface 52Aso as to introduce light also from here. By doing so, it is possible tomake the prism surface 16 more bright and improve in uniformity abrightness distribution on said prism surface 16.

[0165] Next, a direct back light type surface light source device 60 isdescribed with reference to FIG. 14.

[0166] This surface light source device 60 has a light diffusing sheet62 disposed along the coating layer 18 on the reverse side of theoptical sheet 10 shown in FIG. 1, and outputs through said lightdiffusing sheet 62 a light inputted from the light source 54 directlyand after making the light reflect from a concave reflector plate 64.

[0167] In the surface light source device 60 also, in the same manner assaid surface light source device 50, since the distance between thesurface of the coating layer 18 of the optical sheet 10 and the lightdiffusing sheet 62 is controlled to 1 to 10 μm by the spherical beads20, no interference fringes are generated between them. And thespherical beads 20 hardly damage the light diffusing sheet 62.

[0168] A thin metal sheet deposited with aluminum or the like, or awhite foaming polyethylene terephtalate (PET) or the like is used forsaid optical reflector plates 56 and 64.

[0169] A shape capable of uniformly making the light reflect from thelinear light source 54 as parallel rays is enough as the shape of theoptical reflector plate 64 in the direct back light type surface lightsource device 60, and a concave circular arc, a paraboloidal cylinder, ahyperboloidal cylinder, an ellipsoidal cylinder or the like is selected.

[0170] Although the coating layer 18 of the optical sheet 10 is disposeddirectly on the light outputting surface 52B of the light guide means 52in said surface light source device 50, the present invention is notlimited to this but a light diffusing sheet 66 may be disposed betweenthe optical sheet 10 and the light outputting surface 52B in a similarmanner to the surface light source device 50A shown in FIG. 15.

[0171] Although each of the coating layers 18 in said optical sheets isdisposed so as to face the light input side, it may be disposed so thatthe unit prism 14 side faces the light outputting surface 52B side ofthe light guide means 52 or the optical reflector plate 64 side in asimilar manner to surface light source devices 50B and 60A shown inFIGS. 16 and 17.

[0172] Although each of said surface light source devices 50, 50A, 50B,60 and 60A uses a single optical sheet 10, the present invention is notlimited to this but may use a lamination of two, three or more opticalsheets as shown in FIGS. 18 to 21. Even in case of using a lamination ofplural optical sheets in such a way, since variation in height of thespherical beads 20 projecting from the reverse surface of an opticalsheet is a little, no concentrated load damages unit prisms of anotheroptical sheet.

[0173] A surface light source device 70A of FIG. 18 is obtained bydisposing a second optical sheet 72 between the light outputting surface52B of the light guide means 52 and the optical sheet 10 in the surfacelight source device 50 shown in FIG. 13.

[0174] The second optical sheet 72 has basically the same composition assaid optical sheet 10, but its coating layer side is not provided withspherical beads and is formed into a flat and smooth surface similarlyto the prior art.

[0175] The ridge-lines 74A of unit prisms 74 in the second optical sheet72 are arranged perpendicularly to the ridge-lines 14A of the unitprisms 14 in said optical sheet 10.

[0176] In case of the surface light source device 70A, interferencefringes are generated between the flat and smooth surface opposite tothe prism surface of the second optical sheet 72 and the lightoutputting surface 52B of the light guide means 52, but thanks tocovering the upper side of the second optical sheet 72 with the opticalsheet 10, the interference fringes could not be observed.

[0177] A surface light source device 70B shown in FIG. 19 has beenformed out of the composition of FIG. 18 into a direct back light type,and description of it is omitted by giving the same symbols to the samecomponents as FIGS. 14 and 18.

[0178] In such surface light source devices 70A and 70B each having alamination of two prism sheets as described above, the second prismsheet 72 is disposed so that its unit prisms 74 face the lightoutputting surface side, but the present invention is not limited tothis but the unit prisms 74 of the second optical sheet 72 may face thelight guide means 52 side or the light diffusing sheet 66 side,similarly to surface light source devices 70C and 70D shown in FIGS. 20and 21 for example.

[0179] In FIGS. 20 and 21, description of them is omitted by giving thesame symbols to the same components as FIGS. 18 and 19.

[0180] Next, a liquid crystal display apparatus 80 according to anembodiment of the present invention as shown in FIG. 22 is described.

[0181] The liquid crystal display apparatus 80 is formed by arranging aliquid crystal panel 82 at the light outputting surface side of thesurface light source device 50, 50A, 50B, 70 or 70A as shown in FIG. 13,15, 16, 18 or 20.

[0182] This liquid crystal display apparatus is of a light-transmissivetype, and each of pixels forming its liquid crystal screen isilluminated from the back side with the output light from said surfacelight source device.

[0183] In this liquid crystal display apparatus 80, as described above,since no interference fringes appear in the illuminating light from thesurface light source device, a good image can be formed. And since thedistance between the coating layer 18 of the optical sheet 10 and theflat and smooth surface of the light guide means 52, the light diffusingsheet or another optical sheet is 10 μm or less as described above, alight collecting performance, for example, in the normal direction tothe optical sheet 10 is not deteriorated and therefore a good brightnesscan be obtained.

[0184] Next, a surface light source device 90 according to an embodimentof the present invention is described with reference to FIG. 23.

[0185] This surface light source device 90 is provided with the opticalsheet 30 shown in FIG. 8 bringing its coating layer 18 side into contactwith the prism surface of the prism sheet 36 at the light outputtingsurface side, and comprises a light guide means 52 which is aplate-shaped member made of a light-transmissive material similar to thesurface light source device 50 of FIG. 13 and outputs from the upperlight outputting surface 52B a light introduced through the left sideend surface 52A in FIG. 23, a linear light source 54 which is disposedalong and in parallel with said side end surface 52A of this light guidemeans 52 and inputs a light into said light guide means 52 through saidside end surface 52A, and an optical reflector plate 56 which isdisposed so as to cover the opposite surface of said light guide means52 to the light outputting surface 52B and the other side end surfacesthan the left side end surface 52A, and reflects and returns lightsoutputted from these surfaces into the light guide means 52. Said lightguide means 52 is usually accommodated in an enclosure (not illustrated)having the light outputting surface 52B as a window.

[0186] In the surface light source device 90, as described above, sincethe spherical beads 20 are 1 μm or less in half bandwidth of thedistribution of particle diameters, variation in height of the sphericalbeads 20 projecting from the surface of the coating layer 18 is 1 μm orless.

[0187] Therefore, since the spherical beads 20 uniformly come intocontact with the prism tops of the prism sheet 36, a concentrated loadcaused by contact with a greatly projected spherical bead is notgenerated and so damage of the prisms of the prism sheet 36 isprevented.

[0188] And also in case that there is not the prism sheet 36 in FIG. 23,namely, in case that the coating layer 18 of said optical sheet 30 is incontact with the light outputting surface 52B of said light guide means52, similarly the light guide means 52 is prevented from being damaged.

[0189] The material, shape, light diffusing function and light source ofsaid light guide means 52 are the same as the light guide means of saidFIG. 13.

[0190] Next, a direct back light type surface light source device 92 isdescribed with reference to FIG. 24.

[0191] This surface light source device 92 has a prism sheet 36 disposedalong the coating layer 18 on the reverse side of the optical sheet 30shown in FIG. 8 and outputs to said prism sheet 36 a light, which hasbeen inputted from the light source 54, directly and after making thelight reflect from a concave reflector plate 64.

[0192] In the surface light source device 92 also, the spherical beads20 of the coating layer 18 of the optical sheet 30 hardly damage theprism surface.

[0193] Although each of said prism sheets 36 is disposed so that itsprism surface faces the light outputting side, it may be disposed sothat the unit prism 34 side faces the light outputting surface 52B sideof the light guide means 52 or the optical reflector plate 64 side inthe same way as surface light source devices 90A and 92A shown in FIGS.25 and 26.

[0194] Although each of said surface light source devices 90, 90A, 92and 92A uses a single prism sheet, the present invention is not limitedto this but may use a lamination of two, three or more prism sheets asshown in FIGS. 27 to 30. Even in case of using a lamination of pluralprism sheets in such a way, since variation in height of the sphericalbeads 20 projecting from the reverse surface of a prism sheet is alittle, no concentrated load damages unit prisms of another prism sheet.

[0195] A surface light source device 90B of FIG. 27 is formed bydisposing a second optical sheet 96 between the light outputting surface52B of the light guide means 52 and the optical sheet 30 in the surfacelight source device 90 shown in FIG. 23.

[0196] The second optical sheet 96 has basically the same composition assaid optical sheet 30, but may have various unit prisms as shown inFIGS. 4 and 5.

[0197] The ridge-lines 98A of unit prisms 98 in the second optical sheet96 are arranged perpendicularly to the ridge-lines 34A of the unitprisms 34 in said optical sheet 30.

[0198] A surface light source device 92B shown in FIG. 28 is formed byforming the composition of FIG. 27 into a direct back light type, anddescription of it is omitted by giving the same symbols to the samecomponents as FIGS. 27 and 24.

[0199] In such surface light source devices 90B and 92B each having alamination of two prism sheets as described above, the second prismsheet 96 is disposed so that its unit prisms 98 face the lightoutputting surface side, but the present invention is not limited tothis but the unit prisms 98 of the second optical sheet 96 may face thelight guide means 52 side or the light diffusing sheet side, similarlyto surface light source devices 90C and 92D shown in FIGS. 29 and 30 forexample.

[0200] In FIGS. 29 and 30, description of them is omitted by giving thesame symbols to the same components as FIGS. 27 and 28.

[0201] Next, a liquid crystal display apparatus 100 according to anembodiment of the present invention as shown in FIG. 31 is described.

[0202] The liquid crystal display apparatus 100 is formed by arranging aliquid crystal panel 102 at the light outputting surface side of thesurface light source device 90, 90A, 90B or 90C as shown in FIG. 23, 25,27 or 29.

[0203] This liquid crystal display apparatus is of a light-transmissivetype, and each of pixels forming its liquid crystal screen isilluminated from the back side with the output light from said surfacelight source device 90, 90A, 90B or 90C.

[0204] In this liquid crystal display apparatus 100, as described above,since no interference fringes appear in the illuminating light from thesurface light source device, a good image can be formed.

[0205] (Embodiment)

[0206] Next, an embodiment of the present invention is described.

[0207] The optical sheet 10 uses an optical sheet which is made byapplying a transparent adhesive layer of about 1 μm in thickness onto atransparent biaxially-extended PET film (125 μm in thickness), andapplying an ultraviolet-setting resin having as its main ingredient aprepolymer of epoxy acrylate for forming a pattern of unit prisms ontoit, and then mold-releasing the coating resin film after it has beenhardened and which has unit prisms 14 arranged adjacently to one anotherso that their ridge-lines 14A are in parallel with one another atintervals of 30 μm, each of said unit prisms being an isosceles having avertical angle of 85° in section. The spherical beads 20 are disposed inthe following manner on the opposite (reverse) surface to the prismsurface 16 of the transparent base sheet 12 having the unit prisms 14formed on it.

[0208] A coating material composed of light-transmissive beads of abridge-structured acryl resin (refractive index n=1.49) having anaverage particle diameter of 5 μm as a material for the spherical beads20 and a polyester resin (refractive index n=1.55) as a binder isapplied.

[0209] Concretely, an ink containing said light-transmissive beads by 8%of said binder is diluted with a solvent of “MET:toluene=1:1 ” to aviscosity of 27 seconds in Zahnkapp's viscometer #3.

[0210] This ink is applied to the reverse surface of the transparentbase sheet 12 having the unit prisms 14 formed on its obverse surface bymeans of a slit reverse coating method and then the solvent is dried toharden the coated film.

[0211] The spherical beads 20 having a 10-point average roughness Rz of3 μm according to JIS B0601 in the Japanese Industrial Standards havebeen formed in a two-dimensionally random distribution having an averageinterval d of 30 μm.

[0212] When observing an optical sheet 10 formed in such away, forexample, in a state where it is in contact with the light outputtingsurface of the light guide means 52 in a darkroom, no interferencefringes have been observed.

[0213] The following table 1 shows the result of observing a surfacelight source device, as shown in FIGS. 13 to 21, having each of opticalsheets built in it, which optical sheets have the light-transmissivebeads having the various average particle diameters and are similar tothe above-mentioned optical sheets. TABLE 1 10-point Average beadsaverage Interference Diameter roughness R_(z) fringe Embodiment 1 5 μm 3μm No Embodiment 2 3 2 No Embodiment 3 1.5 1 No Embodiment 4 8 5 NoEmbodiment 5 10 7 No Comparison 15 9 Observed Example 1

[0214] As a result, interference fringes have been observed only in thecomparison example 1 in Table 1.

[0215] When a single optical sheet of embodiment 1 in Table 1 and anoptical sheet having the obverse surface having unit prisms each ofwhich is an isosceles-triangular prism whose vertical angle is 90° andthe reverse surface which is flat and smooth are assembled, as shown inFIG. 16, in said surface light source device, an exemplary embodiment isobtained.

[0216] As a result of experiments in which an optical sheet coated withspherical beads 20 having a particle diameter distribution according tothe present invention and an optical sheet coated with spherical beads20A having another particle diameter distribution more greatly varyingin particle diameter are respectively dragged, for example, in a statewhere the spherical beads side of each of them is in contact with aprism surface and a 10-g weight is put on it, the greater the particlediameter distribution is in variation in particle diameter, the moreflaws have been generated.

[0217] Particularly, when the half bandwidth of the distribution ofparticle diameters is 1 μm or less, flaws on the prism surface areremarkably small in number.

[0218] A light diffusing layer 32 of the optical sheet 30 which is alight diffusing sheet is formed by applying a coating material composedof light-transmissive beads of a bridge-structured acryl resin(refractive index n=1.49) having an average particle diameter of 5 μm asa material for the spherical beads and a polyester resin (refractiveindex n=1.55) as a binder.

[0219] The coating layer 18 containing the spherical beads 20 isdisposed on the opposite (reverse) surface to the light diffusing layer32 of this transparent base sheet 12, in the following manner similarlyto said embodiment.

[0220] When observing an optical sheet 30 formed in such a way, forexample, in a state where it is in contact with the light outputtingsurface of the light guide means 52 in a darkroom, no interferencefringes have been observed.

[0221] The prism sheet 36 uses an optical sheet which is made byapplying a transparent adhesive layer of about 1 μm in thickness onto atransparent biaxially-extended PET film (125 μm in thickness), andapplying an ultraviolet-setting resin having as its main ingredient aprepolymer of epoxy acrylate for forming a pattern of unit prisms ontoit, and then mold-releasing the coating resin film after it has beenhardened and which has unit prisms 14 arranged adjacently to one anotherso that their ridge-lines 14A are in parallel with one another atintervals of 30 μm, each of said unit prisms being an isosceles having avertical angle of 85° in section.

[0222] A result of observing a surface light source device, as shown inFIGS. 23 to 30, having each of optical sheets built in it, which opticalsheets have the light-transmissive beads having the various averageparticle diameters and are similar to the above-mentioned lightdiffusing sheet, has shown the same result as the table 1 as describedabove.

[0223] When a single optical sheet which is a light diffusing sheetcorresponding to embodiment 1 in Table 1 and a prism sheet which has theobverse surface having unit prisms each of which is anisosceles-triangular prism whose vertical angle is 90° are assembled asshown in FIG. 23, such defects as flaws and the like of the opticalsheet have been covered and an optical distribution of the output lighthas been made more smooth.

[0224] As a result of experiments in which an optical sheet which is alight diffusing sheet coated with spherical beads 20 having a particlediameter distribution according to the present invention and an opticalsheet coated with spherical beads 20A having another particle diameterdistribution more greatly varying in particle diameter are respectivelydragged, for example, in a state where the spherical beads side of eachof them is in contact with a prism surface and a 10-g weight is put onit, the greater the particle diameter distribution is in variation inparticle diameter, the more flaws have been generated.

[0225] Particularly, when the half bandwidth of the distribution ofparticle diameters is 1 μm or less, flaws on the prism surface areremarkably small in number. Further particularly, in case that thevertical angles on the optical sheet are as sharp as 100° or less,damage of the prism surface has been greatly influenced by variation inparticle diameter-of said beads.

What is claimed is:
 1. An optical sheet which has one surface of itslight-transmissive base material on which at least one of a group ofplural unit prisms and a group of plural unit lenses is arranged and theother surface of it coated with a coating layer formed out oflight-transmissive materials, wherein said coating layer is composed ofa light-transmissive resin and light-transmissive fine particlesdispersed in said light-transmissive resin, and at least part of saidfine particles form a number of fine knoll-shaped projections of 1 to 10μm in height projecting from said surface by being projected from theopposite surface of said coating layer to the light-transmissive basematerial.
 2. An optical sheet as defined in claim 1, wherein saidcoating layer is 2 to 20 μm in thickness including said fineknoll-shaped projections.
 3. An optical sheet as defined in claim 1,wherein said fine knoll-shaped projections are disposed at random alongsaid surface of said coating layer.
 4. An optical sheet as defined inclaim 1, wherein at least part of said fine particles are composed oflight-transmissive beads of 1 to 10 μm in particle diameter.
 5. Anoptical sheet as defined in claim 1, wherein said fine particles arespherical beads of 1 μm or less in half bandwidth of the distribution ofparticle diameters.
 6. An optical sheet as defined in claim 1, whereinthe ratio of the refractive index of a material forming said fineparticles to the refractive index of a light-transmissive resin in saidcoating layer is 0.9 to 1.1.
 7. An optical sheet as defined in claim 1,wherein said coating layer is formed by applying and drying an ink tothe reverse surface of said light-transmissive base material, said inkbeing obtained by mixing with each other said light-transmissive resinand said light-transmissive beads less in specific gravity than saidresin, and said fine knoll-shaped projections are formed by projectingsaid light-transmissive beads from said ink-coated film which has driedand contracted.
 8. An optical sheet as defined in claim 1, wherein atleast part of fine particles are formed out of light-transmissive beads,and said light-transmissive beads are distributed unevenly more at theopposite surface side of said coating layer to the light-transmissivebase material and projected from said opposite surface.
 9. An opticalsheet as defined in claim 8, wherein said coating layer is formed byapplying an ink obtained by mixing with each other saidlight-transmissive resin and said light-transmissive beads less inspecific gravity than said resin to the reverse surface of saidlight-transmissive base material so as to be pressed by gravity, and byhardening the ink after said light-transmissive beads come to bedistributed unevenly more in the vicinity of the surface after the inkhas been applied.
 10. An optical sheet which has one surface of itslight-transmissive base material on which at least one of a group ofplural unit prisms and a group of plural unit lenses is arranged and theother surface of it coated with a coating layer formed out oflight-transmissive materials, wherein said coating layer is composed ofa light-transmissive resin and light-transmissive beads which aredispersed in said light-transmissive resin, 1 to 10 μm in particlediameter and 1 μm or less in half bandwidth of the distribution ofparticle diameters, and at least part of said light-transmissive beadsare projected from the opposite surface of said coating layer to thelight-transmissive base material and thereby many fine knoll-shapedprojections of 1 to 10 μm in height projecting from said surface areformed and said coating layer is formed to be 2 to 20 μm in thicknessincluding said fine knoll-shaped projections, and the ratio of therefractive index of a material forming said light-transmissive beads tothe refractive index of the light-transmissive resin in the coatinglayer is 0.9 to 1.1.
 11. An optical sheet as defined in claim 10,wherein said light-transmissive beads are distributed unevenly more atthe opposite surface side of said coating layer to thelight-transmissive base material and projected from said oppositesurface.
 12. An optical sheet having a light-transmissive base materialhaving one surface having a light diffusing layer and the other surfacecovered with a coating layer formed out of a light-transmissivematerial, said coating layer comprising light-transmissive sphericalbeads of 1 μm or less in half bandwidth of the distribution of particlediameters.
 13. An optical sheet as defined in claim 12, wherein saidlight diffusing layer is formed so as to contain light-transmissivebeads, and the average particle diameter of the light-transmissivespherical beads in said light diffusing layer is made larger than theaverage particle diameter contained in said coating layer.
 14. Anoptical sheet as defined in claim 12, wherein the spherical beadscontained in said coating layer are 1 to 10 μm in particle diameter. 15.An optical sheet lamination which is formed by laminating togetherplural optical sheets containing unit prisms or unit lenses, whereineach optical sheet has plural unit prisms or unit lenses arranged on onesurface of a light-transmissive base material and the other surfacebeing covered with a coating layer formed out of a light-transmissivematerial, said coating layer contains light-transmissive spherical beadsof 1 μm or less in half bandwidth of the distribution of particlediameters, and said coating layer in the laminated optical sheet is incontact with unit prisms or unit lenses on an adjacently laminatedoptical sheet.
 16. An optical sheet lamination as defined in claim 15,wherein the vertical angle of the tops of the prisms or lenses onanother optical sheet in contact with the coating layer is as sharp asin 100° or less.
 17. An optical sheet lamination which is formed bylaminating together one or more optical sheets each of which has alight-transmissive base material having one surface having a lightdiffusing layer and the other surface covered with a coating layerformed out of a light-transmissive material, said coating layer containslight-transmissive spherical beads of 1 μm or less in half bandwidth ofthe distribution of particle diameters, and one or more optical sheetseach of which has plural unit prisms or plural unit lenses arranged onthe surface of a light-transmissive base material, wherein said coatinglayer in an laminated optical sheet is in contact with unit prisms orunit lenses on another optical sheet laminated adjacently to saidlaminated optical sheet.
 18. An optical sheet lamination as defined inclaim 17, wherein the vertical angle of the tops of the prisms or lenseson another optical sheet in contact with the coating layer is as sharpas in 100° or less.
 19. A surface light source device composed of alight source for outputting light from its light outputting surface andan optical sheet provided adjacently to said light outputting surface,said optical sheet having one surface of a light-transmissive basematerial on which at least one of a group of plural unit prisms and agroup of plural unit lenses is arranged and the other surface beingcovered with a coating layer formed out of light-transmissive materials,wherein said coating layer is composed of a light-transmissive resin andlight-transmissive fine particles dispersed in said light-transmissiveresin, and at least part of said fine particles are formed into manyfine knoll-shaped projections of 1 to 10 μm in height projecting fromsaid surface by being projected from the opposite surface of saidcoating layer to the light-transmissive base material.
 20. A surfacelight source device as defined in claim 19, wherein said coating layeris 2 to 20 μm in thickness including said fine knoll-shaped projections.21. A surface light source device as defined in claim 19, wherein atleast part of said fine particles are light-transmissive beads of 1 to10 μm in particle diameter.
 22. A surface light source device as definedin claim 19, wherein said fine particles of the coating layer in saidoptical sheet are spherical beads of 1 μm or less in half bandwidth ofthe distribution of particle diameters.
 23. A surface light sourcedevice as defined in claim 19, wherein the ratio of the refractive indexof a material forming said fine particles to the refractive index of alight-transmissive resin in the coating layer is 0.9 to 1.1.
 24. Asurface light source device as defined in claim 19, wherein at least onelens sheet which has one surface of a light-transmissive base materialon which at least one of a group of plural unit prisms and a group ofplural unit lenses is arranged and the other surface being made flat andsmooth without raggedness by being covered with a coating layer formedout of a light-transmissive material is put between said optical sheetand said light outputting surface.
 25. A surface light source device asdefined in claim 19, wherein said light source is composed of a lightguide means which is a plate-shaped member one of whose surfaces is saidlight outputting surface and which outputs a light introduced through atleast one side end surface from said light outputting surface, and alight generating source for inputting light into said light guide meansthrough at least said one side end face of said light guide means.
 26. Asurface light source device as defined in claim 19, wherein a lightdiffusing sheet is disposed on the light outputting surface of saidlight source and the light outputted through said light diffusing sheetfrom said light outputting surface is inputted from said coating layerside.
 27. A surface light source device as defined in claim 19, whereinat least part of said fine particles are formed out oflight-transmissive beads, and said light-transmissive beads aredistributed unevenly more at the opposite surface side of said coatinglayer to the light-transmissive base material and are formed into manyfine knoll-shaped projections by being projected from said surface. 28.A surface light source device as defined in claim 19, wherein thevertical angle of the tops of the prisms or lenses on another opticalsheet in contact with the coating layer is as sharp as in 100° or less.29. A surface light source device composed of a light source foroutputting light from its light outputting surface and an optical sheetprovided adjacently to said light outputting surface, said optical sheethaving one surface of a light-transmissive base material on which atleast one of a group of plural unit prisms and a group of plural unitlenses is arranged and the other surface being covered with a coatinglayer formed out of light-transmissive materials, wherein said coatinglayer comprises light-transmissive spherical beads of 1 μm or less inhalf bandwidth of the distribution of particle diameters and the lightoutputted from said light outputting surface is inputted from saidcoating layer side.
 30. A surface light source device as defined inclaim 29, wherein said light diffusing layer compriseslight-transmissive spherical beads, and the average particle diameter ofthe light-transmissive spherical beads in said light diffusing layer islarger than the average particle diameter of the spherical beadscontained in said coating layer.
 31. A surface light source device asdefined in claim 29, wherein the spherical beads contained in saidcoating layer are 1 to 10 μm in particle diameter.
 32. A surface lightsource device as defined in claim 29, wherein the vertical angle of thetops of the prisms or lenses on another optical sheet in contact withthe coating layer is as sharp as in 100° or less.
 33. A surface lightsource device composed of a light source for outputting light from itslight outputting surface and an optical sheet provided adjacently tosaid light outputting surface, said optical sheet having one surface ofa light-transmissive base material on which at least one of a group ofplural unit prisms and a group of plural unit lenses is arranged and theother surface being covered with a coating layer formed out oflight-transmissive materials, wherein said coating layer containslight-transmissive beads, dispersed in said light-transmissive resin, of1 to 10 μm in particle diameter and 1 μm or less in half bandwidth ofthe distribution of particle diameters, and at least part of saidlight-transmissive beads are formed into many fine knoll-shapedprojections of 1 to 10 μm in height projecting from the opposite surfaceof said coating layer to the light-transmissive base material by beingprojected from said opposite surface, and said coating layer is 2 to 20μm in thickness including said fine knoll-shaped projections, and theratio of the refractive index of a material forming saidlight-transmissive beads to the refractive index of thelight-transmissive resin in the coating layer is 0.9 to 1.1.
 34. Asurface light source device as defined in claim 33, wherein saidlight-transmissive beads are distributed unevenly more at the oppositesurface side of said coating layer to the light-transmissive basematerial and projected from said surface.
 35. A surface light sourcedevice as defined in claim 33, wherein the vertical angle of the tops ofthe prisms or lenses on another optical sheet in contact with thecoating layer is as sharp as in 100° or less.
 36. A light-transmissivetype display apparatus composed of a flat light-transmissive displaymeans and a surface light source device which is disposed at the back ofsaid light-transmissive display means and irradiates saidlight-transmissive display means from the back with its output light,wherein said surface light source device is composed of a light sourcefor outputting light from its light outputting surface and an opticalsheet provided adjacently to said light outputting surface, said opticalsheet having one surface of a light-transmissive base material on whichat least one of a group of plural unit prisms and a group of plural unitlenses is arranged and the other surface being covered with a coatinglayer formed out of light-transmissive materials, and light-transmissivefine particles different from a material for the coating layer aredisposed on the opposite surface of said coating layer to thelight-transmissive base material and thereby many fine knoll-shapedprojections of 1 to 10 μm in height projecting from said surface areformed, and the light outputted from said light outputting surface isinputted from said coating layer side.
 37. A light-transmissive typedisplay apparatus as defined in claim 36, wherein said coating layer insaid optical sheet is 2 to 20 μm in thickness including said fineknoll-shaped projections.
 38. A light-transmissive type displayapparatus as defined in claim 36, wherein at least part of said fineparticles in said optical sheet are light-transmissive beads of 1 to 10μm in particle diameter.
 39. A light-transmissive type display apparatusas defined in claim 36, wherein said fine particles of the coating layerin said optical sheet are spherical beads of 1 μm or less in halfbandwidth of the distribution of particle diameters.
 40. Alight-transmissive type display apparatus as defined in claim 36,wherein the ratio of the refractive index of a material forming saidfine particles in said optical sheet to the refractive index of thelight-transmissive resin in the coating layer is 0.9 to 1.1.
 41. Alight-transmissive type display apparatus as defined in claim 36,wherein at least one lens sheet which has one surface of alight-transmissive base material on which at least one of a group ofplural unit prisms and a group of plural unit lenses is arranged and theother surface being made flat and smooth without raggedness by beingcovered with a coating layer of a light-transmissive material is putbetween said optical sheet and said light outputting surface in saidsurface light source device.
 42. A light-transmissive type displayapparatus as defined in claim 36, wherein said light source in saidsurface light source device is composed of a light guide means which isa plate-shaped member, formed out of a light-transmissive material,having one surface of it as said light outputting surface and outputs alight inputted from at least one side end surface through said lightoutputting surface, and a light generating source for inputting lightfrom at least said one side end surface of said light guide means intoit.
 43. A light-transmissive type display apparatus as defined in claim36, comprising a light diffusing sheet on the light outputting surfaceof said light source in it, wherein a light outputted through said lightdiffusing sheet from said light outputting surface is inputted from saidcoating layer side.
 44. A light-transmissive type display apparatus asdefined in claim 36, wherein at least part of said fine particles insaid optical sheet are formed out of light-transmissive beads, and saidlight-transmissive beads are distributed unevenly more at the oppositesurface side of said coating layer to the light-transmissive basematerial, and formed into said many fine knoll-shaped projections bybeing projected from said surface.
 45. A light-transmissive type displayapparatus as defined in claim 36, wherein said vertical angle of thetops of the prisms or lenses on another optical sheet in contact withthe coating layer is as sharp as in 100° or less.
 46. Alight-transmissive type display apparatus provided with a flatlight-transmissive display means and a surface light source device whichis disposed at the back of said light-transmissive display means andirradiates said light-transmissive display means from the back with itsoutput light, wherein said surface light source device is composed of alight source for outputting light from its light outputting surface andan optical sheet provided adjacently to said light outputting surface,wherein said optical sheet has one surface of a light-transmissive basematerial on which a light diffusing sheet is provided and the othersurface being covered with a coating layer of a light-transmissivematerial, and said coating layer contains light-transmissive sphericalbeads of 1 μm or less in half bandwidth of the distribution of particlediameters, and at least part of these spherical beads are projected fromthe opposite surface of said coating layer to the light-transmissivebase material and are formed into many fine knoll-shaped projections of1 to 10 μm in height projecting from said surface, and the lightoutputted from said light outputting surface is inputted from saidcoating layer side.
 47. A light-transmissive type display apparatus asdefined in claim 46, wherein said light diffusing layer in said opticalsheet contains light-transmissive spherical beads, and the averageparticle diameter of the light-transmissive spherical beads in saidlight diffusing layer is made larger than the average particle diameterof the spherical beads contained in said coating layer.
 48. Alight-transmissive type display apparatus as defined in claim 46,wherein said spherical beads contained in said coating layer in saidoptical sheet are 1 to 10 μm in particle diameter.
 49. Alight-transmissive type display apparatus as defined in claim 46,wherein the vertical angle of the tops of the prisms or lenses onanother optical sheet in contact with the coating layer is as sharp asin 100° or less.
 50. A light-transmissive type display apparatusprovided with a flat light-transmissive display means and a surfacelight source device which is disposed at the back of said flatlight-transmissive display means and irradiates said light-transmissivedisplay means from the back with its output light, wherein said surfacelight source device is composed of a light source for outputting lightfrom its light outputting surface and an optical sheet providedadjacently to said light outputting surface, said optical sheet has onesurface of a light-transmissive base material on which at least one of agroup of plural unit prisms and a group of plural unit lenses isarranged and the other surface being covered with a coating layer formedout of light-transmissive materials, said coating layer is composed of alight-transmissive resin and light-transmissive beads which aredispersed in said light-transmissive resin and are 1 to 10 μm inparticle diameter and 1 μm or less in half bandwidth of the distributionof particle diameters, and at least part of said light-transmissivebeads are formed into many fine knoll-shaped projections of 1 to 10 μmin height projecting from the opposite surface of said coating layer tothe light-transmissive base material by being projected from saidsurface, and said coating layer is 2 to 20 μm in thickness includingsaid fine knoll-shaped projections, and the ratio of the refractiveindex of a material forming said light-transmissive beads to therefractive index of the light-transmissive resin in said coating layeris 0.9 to 1.1.
 51. A light-transmissive type display apparatus asdefined in claim 50, wherein said light-transmissive beads in saidoptical sheet are distributed unevenly more at the opposite surface sideof said coating layer to the light-transmissive base material and areprojected from said surface.
 52. A light-transmissive type displayapparatus as define in claim 50, wherein the vertical angle of the topsof the prisms or lenses on another optical sheet in contact with thecoating layer is as sharp as in 100° or less.